Method of and an apparatus for determining an optimum schedule of operation for reversible hot rolling mills

ABSTRACT

A method of and an apparatus for determining such an optimum schedule of operation as to provide a shortest total rolling time for reversible hot rolling mills, wherein an initial schedule of operation for initial passes is determined based upon the properties of a material to be rolled, rolling conditions and standard resistance to deformation of the material, and based upon the actual resistance to deformation obtained in the initial passes, an optimum schedule of operation for subsequent passes is determined so that it provides a shortest total rolling time.

United States Patent Minami et al.

[54] METHOD OF AND AN APPARATUS FOR DETERMINING AN OPTIMUM SCHEDULE OF OPERATION FOR REVERSIBLE HOT ROLLING MILLS [72] Inventors: Tohru Minami; Mikio Nishio, both of Sakai-shi; Ichiro Toyama, Kisarazu-shi; Shigeyoshi Kawano,

Hitachi-shi; Masumi Imai, Hitachishi; Yutaka Takuma, Hitachi-shi; Hidehiro Kitanosono, Hitachishi, all

of Japan [73] Assignee: Hitachi, Ltd., and Yowata Iron &

Steel Co., Ltd., Tokyo, Japan [22] Filed: Aug. 20, 1969 211 Appl. No.: 851,622

[30] Foreign Application Priority Data Feb. 8, 1969 Japan ..44/9407 52 US. Cl ..72/6, 72/8 51] Int. Cl. ..B21b 37/00 [58] FieldofS earch ..72/6-10, 16,21,

[ 1 Sept. 5, 1972 [56] References Cited UNITED STATES PATENTS 3,177,346 4/1965 Green ..72/8 X 3,332,263 7/1967 Beadle et a1. ..72/7 3,543,548 12/1970 Smith, Jr. ..72/7 3,104,566 9/1963 Schurr et a1. ..72/27 X 3,253,438 5/1966 Stringer ..72/12 3,289,444 12/ 1966 Takuma ..72/7

Primary ExaminerMilton S. Mehr Attorney-Craig, Antonelli & Hill [57 ABSTRACT A method of and an apparatus for determining such an optimum schedule of operation as to provide a shortest total rolling time for reversible hot rolling mills, wherein an initial schedule of operation for initial passes is determined based upon the properties of a material to be rolled, rolling conditions and standard resistance to deformation of the material, and based upon the actual resistance to deformation obtained in the initial passes, an optimum schedule of operation for subsequent passes is determined so that it provides a shortest total rolling time.

7 Claims, 11 Drawing Figures SVdZ x,

PATENTEDSEP 19 2 3.688.555

sum 1 or 5 F/GT/a METHOD OF AND AN APPARATUS FOR DETERMINING AN OPTIMUM SCHEDULE OF OPERATION FOR REVERSIBLE I'IOT ROLLING MILLS schedule by means of a computer that is applied to a fully automated operation of a hot rolling mill.

In conventional manual operation of blooming mills, the rolling schedules have been prepared from experiences of years of operations, and in such cases only one schedule was prepared for obtaining a slab of specified dimensions from an ingot specified dimensions.

However, since the load applied to a driving motor differs according to the soaking temperature of an ingot to be rolled even in a same rolling condition, the sole schedule must be prepared to be applicable in spite of any possible deviation of the soaking temperature of ingots. This fact means that the driving motor will usually be operated with an excess i.e., spare, capacity, and therefore the rolling schedule can not be said to be an optimum one for obtaining the largest rolling capacity for a particular soaking temperature of an ingot. Such deviations of the schedule from the optimum condition have been compensated by proper modifications of the schedule based upon the experiences of skilled operators.

Therefore, when a rolling schedule is determined by a computer as in this invention, the schedule must be so determined as to provide the largest rolling capacity for a particular soaking temperature of an ingot to be rolled.

Accordingly, the object of this invention is to provide a method of searching for and determining a rolling schedule which enables one to obtain the largest rolling capacity for a particular nature and soaking temperature of an ingot which will satisfy various limitations regarding ingots and a rolling plant as well as the finished shapes and dimensions of slabs.

To accomplish the above-mentioned object, this invention has a first feature that an initial rolling schedule for an initial several passes is determined prior to the operation based upon an estimated soaking temperature of an ingot (or resistance to deformation of an ingot), the initial passes are performed according to the initial schedule, the rolling load or motor torque at a roll stand is measured during the initial passes, and a rolling schedule for the subsequent passes is determined based upon the soaking temperature or resistance to deformation of the ingot computed from the measured roll load or motor torque.

A second feature of this invention is that a plurality of rolling schedules are computed by varying the amount of such a portion of an available motor torque that is available as a rolling torque thereby to determine an optimum schedule which provides a shortest rolling time.

According to a third feature of this invention, an optimum rolling schedule which provides a shortest total rolling time is determined by such a process that a plurality of schedules of rolling operation are computed by gradually decreasing the limit of available rolling torque starting from the maximum value of the available motor torque, and a schedule which. had been obtained just before the number of total rolling passes was increased or a schedule which was obtained at last when the number of total rolling passes was not increased even when the limit of available rolling torque has been decreased to a predetermined lower limit is adopted as an optimum schedule which provides a shortest total rolling time.

In the accompanying drawings;

FIG. la is a diagrammatic illustration of a control system for a universal blooming mill;

FIG. 1b is a diagram showing a pattern of a speed instruction for a horizontal roll stand in FIG. la;

FIG. 2 is a block diagram for computing an initial schedule of rolling operation;

FIG. 3 is a diagram showing the behavior of the resistance to deformation different of ingots;

FIG. 4 is a block diagram for computing subsequent schedules of rolling operation;

FIG. 5 is a block diagram showing the process of determining a schedule of rolling operation for a pass at a roll stand;

FIG. 6 is a diagram showing a relation between the speed-torque performance of an electric motor and the limit of rolling torque;

FIG. 7 is a diagram showing the method of obtaining a schedule for a shortest total rolling time;

FIG. 8 is a diagram showing the effect of the resistance to deformation to a shift of the optimum schedule;

FIG. 9 is a diagram showing the effect of the limit of reduction rate to a shift of the optimum schedule; and

FIG. 10 is a diagrammatic illustration showing the details of device for determining an optimum subsequent schedule.

In FIG. 1a, a blooming mill is shown diagrammatically with its ingot receiving table 1, slab delivery table 2, a pair of vertical rolls 3, and a pair of horizontal rolls 4, wherein a material 5 is being rolled. The vertical and horizontal roll pairs are respectively driven by driving means designated by reference numerals 6 and 7, which are controlled by speed instruction signals N and N respectively, wherein the suffix i shows the order of pass. Since it is required that the ratio of speeds of the vertical and horizontal rolls is kept at a determined value DCi, which is called the draft compensating rate, the speed instruction signal N for the vertical rolls is computed from DCi and N as N DCi- N by a multiplier 8. The draft compensating rate is expressed by the following general formula:

DCi K Fl/AMI wherein K is a constant, A is the cross-sectional area of the material at a section perpendicular to the longitudinal axis of the material when positioned between the vertical and horizontal rolls during the i-th pass, and A is the cross sectional area of the material after the completion of the i-th passage.

The roll openings of the vertical and horizontal roll pairs 3 and 4 are adjusted by opening adjusting means 14 and 15, respectively, which are subjected to opening instruction signals S and S respectively.

Signals of S S N and DCi are supplied from an automatic operation control means 400. The speed instruction signal N for the horizontal roll pairs 4 is generally so controlled that the speed diagram of the roll pair takes such a pattern as shown in FIG. 1b. In the beginning, the roll pair is accelerated up to an entry speed Net, and at this speed, a material is entered into the pair of rolls. Then, the rolls are accelerated up to a maximum speed N with an acceleration AC1, which can be optionally determined or selected from several predetermined values. The speed of the rolls is then decreased at a proper time determined by the automatic operation control means 400 to a delivery speed Ndl, and at this speed, the material is discharged from the roll pair. At the completion of the i-th pass, the opening adjusting means 14 and 15 receive the next instruction signals S l and S I, respectively, and after the adjustment of the roll openings, the (i+l )-th pass is started by the automatic operation control means 400.

in the above-mentioned manner, the automatic operation of the blooming mill is continued under the control of the control means 400, while data necessary for the automatic operation such as S S N N ACi, DCi (called hereinunder PSi in general term) are provided by a rolling schedule determining means 300. The means 309 also provides an automatic operation starting or stopping signal SP to the means 400.

The gist of this invention is, therefore, to provide the above-mentioned rolling schedule determining means 309 which provides an optimum schedule PSi to the automatic operation control means 460 for obtaining the largest rolling capacity of a blooming mill.

The rolling schedule determining means 300 includes an initial schedule determining means 100 which determines an initial schedule PS1" (1' l =j, j being the order of the last pass of the initial passes) for the initial passes according to a signal FR for demanding the determination of the initial schedule and various data CD regarding material and rolling conditions. The means 100 provides the automatic operation starting signal SP and the initial schedule PSi' to the means 400 to start the rolling operation of the initial passes. The initial schedule PSi' is also supplied to an initial schedule storing means 1 16 and is stored therein.

Reference numeral 150 designates an actual data collecting means to which are fed actual opening Sy of the vertical roll pair 3 obtained from a detector 16, actual opening S of the horizontal roll pair 4 obtained from a detector 17, load of the vertical rolls P obtained from a detector 18, load of the horizontal rolls P obtained from a detector 19, torque signal of the vertical rolls r obtained from a detector 20 and torque signal of the horizontal rolls 1 obtained from a detector 21, the last two signals being used as a substitute for the load signals P P When the load detectors l8, 19 are not installed the torques detected by the detectors 2%, 21 are used as a substitute for the load signals. Even when the load detectors 18, 19 are installed, if the detected values P P are not reasonable and values r r are considered to be reasonable (for instance, if load signals are zero because of detecting failure), the torque signals are used Thus it will be appreciated that there is a relation between the load and the torque which is shown in formula (2), appearing hereinafter.

The actual data collecting means 150 supplies the collected data to a data storing means 160, and when the actual data of a predetermined k-th passage (2 g k i j M, wherein j is the number of the initial rolling passes, and M is a number of the total passes.) has been collected, dispatches a signal SR for demanding calculation of the schedule of the subsequent passes to a schedule determining means 200. The means 200 calculates and determines an optimum rolling schedule PSi" for the subsequent passes comprising the 0+1 )-th to M-th passes based upon the actual data of the initial passes stored in the data storing means 160, the data stored in the initial schedule storing means 110 and other various rolling specification CD, wherein as the actual data are not obtained beyond the k-th pass because of k j, the data of the (k+l)-th to j-th passes are assumed to be equal to the predetermined values stored in the means 110. The optimum rolling schedule PSi" is supplied to the automatic operation control means 400 for automatic operation of the mill.

As previously described, for the preparation of rolling schedules, the soaking temperature or the resistance to deformation of an ingot is an only unknown factor. Therefore, when an initial rolling schedule is prepared of an ingot prior to the rolling operation thereof, the initial schedule determining means is supplied with data A which are known and relate to constant properties of the ingot, data B regarding rolling conditions, data C regarding various limitational conditions and data Ss regarding standard resistance to deformation of the ingot at a standard soaking temperature, as shown in FIG. 2, to obtain a schedule PSi for the initial passes. However, in this case, a value of about 20 per cent over of a standard resistance to deformation is used as the input of the resistance to deformation for the purpose of safety. The data C regarding various limitational conditions include those for the passes, initial passes and subsequent passes.

The initial schedule determining means 100 determines a set of initial schedule for the first and second, or in some cases the first, second and third passes, which accomplishes a largest reduction rate within the limitation conditions imposed by the above-mentioned data, without considering the rolling efficiency at the instant. The initial schedule PSi' thus obtained is supplied to the automatic operation control means 400 together with the rolling operation starting signal SP as shown in H6. 2, whereupon the initial passes of the rolling operation are started. The object of the initial passes (generally the first to j-th passes) is to obtain actual rollin g data for determining the actual resistance to deformation of an ingot, which is necessary to determine an optimum rolling schedule for the subsequent passes.

In the first pass, wherein an ingot is passed from left to right seen in FIG. la, the main object of the rolling is to remove scales and a taper of the ingot which generally has a shape of a truncated pyramid, and therefore, no highly reliable data for determining the resistance to deformation can be obtained in the first pass. in the second pass, however, wherein the ingot will already have a regular shape with little scale, the data obtained are usually highly reliable.

Therefore, in the second pass, wherein the ingot is passed from right to left seen in H6. la, roll load or motor torque at the horizontal rolls is measured while the ingot is rolled at the horizontal roll stand, and from the measured value, the resistance to deformation of P1112 f b- /R-Ah (1 where P, actual load at the horizontal rolls in the second pass b width of the material before entrance to the second pass R :radius of the roll Ah reduction by the horizontal rolls in the second pass S resistance to deformation of the material at the time of rolling by thehorizontal rolls in the second pass When the roll load is not obtained, the motor torque 1 which is obtained from the speed of a direct current motor and the amperage, may be used as a substitute for the roll load to calculate the resistance to deformation S by the following formula:

2A VR Ahg where A: torque arm factor ln this case, it is preferable to use a value which is the rest of the total motor torque reduced of an accelerating torque portion, or a real rolling torque in Formula (2).

The object of obtaining the resistance to deformation of the material in the second pass to use the value for estimation of subsequent change of the resistance. On the other hand, as a result of analyses of records of operation of actual machines, we found that the resistance to deformation Sm defined in general form of the above-mentioned Formula (1) is so related with a rate of elongation E length of rolled material on the final pass length of ingot which is the material before rolled) in the rolling direction of a rolled material as shown in FIG. 3.

The curves 0, b and show three different performances of the resistance to deformation due to differences of material and soaking temperature. However, it was found that these curves may be considered as parallel shifts of each other. Therefore, it is assumed that the resistance to deformation is expressed by the following formula:

m m f( c where flE)+e=S,, is called a curve of standard resistance to deformation, and is determined to be, for example, the curve (b) in F IG. 3. e, is a modification factor for the kind of steel. If the actual resistance to deformation S in the second pass is known from Formula (1) and the rate of elongation E2 in the second pass is obtained, cm can be calculated as follows:

By determining the value of e in Formula (3) from Formula (4), the curve of resistance to deformation for the subsequent passes can be derived.

A schedule for the subsequent passes is then determined based upon the resistance to deformation calculated from Formula (3) to give the shortest rolling time. The procedure is shown in FIG. 4. In other words, the subsequent schedule determining means 200 is supplied with data A regarding the properties of the ingot such as dimensions, weight, materiahetc. of the ingot, data B regarding rolling conditions such as'hot finished dimensions determined from cold finished dimensions and margins for safety, shrinkage and scarf, data C regarding various limitational conditions such as limit of roll load, limit of motor torque, various limits of reduction rate such as limit of entry reduction rate, limit of reduction rate for preventing cracking of material determined from material and soaking temperature, and limit of reduction rate applied to later finishing passes .for finishing the material to required dimensions, resistance to deformation S, calculated from Formula (3), and actual roll opening F in the initial passes. Then, the means 200 firstestimates the dimen- .sions of the material at the time of starting calculation of rolling schedule for the subsequent passes, and determines the rolling schedule according to the method as described hereinunder.

As shown in FIG. '5, the amount of reduction is determined in a manner that it is within the various limits of reduction rate as mentioned in the above, and that the rolling torque and the rolling load are also restricted within their limit. By repetition of these procedures for successive passes, values of the reduction rate, rolling torque, rolling load and outlet dimensions of the material are determined, and the outlet dimensions are always checked if they have approached desired target values. Then, if the outlet dimensions have approached the desired target values, a final pass is so determined that the target dimensions are strictly obtained. Thus, a schedule for the subsequent passes is determined.

However, with respect to the rolling schedule obtained in the above-mentioned processes, it is not guaranteed that the schedule is the optimum one for obtaining the highest rolling capacity. In the abovementioned method of determining a rolling schedule, it is the selection of value of the rolling torque limit that has a great influence on the quality of the schedule or the rolling capacity which is accomplished by the schedule. Of various limitational quantities shown in FIG. 5, the rolling torque limit is the only quantity which is left to free selection by the determiner of the schedule, while other limitational quantities are restricted from some objective conditions.

The torque performance of a direct current motor for driving a blooming mill is generally expressed as shown in FIG. 6 by a curve JKL with respect to the motor speed. Therefore, a problem is that how much per cent of the motor torque is to be used as the rolling torque with the rest per cent being used as the accelerating torque, and this allocation has a great in-' fluence on the rolling capacity. If, as an extreme example, the rolling torque is selected to be the full per cent of the motor torque limit or W Oil, a large reduction rate can be obtained, whereby the number of passes is decreased, while on the other hand, since the acceleration torque is zero, the entry speed of the material which is generally low can not be accelerated, and therefore, the rolling time of one pass is very long, resulting in a long total rolling time. On the contrary, if

the rolling torque is selected to be very small, a large torque is available as the accelerating torque, whereby the rolling speed is much increased with a natural shortening of a rolling time. However, since in this case the amount of reduction by one pass is small, the number of passes increases, thus resulting also in an increase of the total roiling time.

. The above-mentioned fact shows that there is an optimum value of the rolling torque limit, and that even if a schedule for a pass is determined to make the rolling time of the pass to be shortest based upon the actual resistance to deformation obtained in the preceding pass, the total rolling time can not necessarily be reduced to the shortest. Therefore, a rolling schedule having the shortest total rolling time can, as a rule, only be obtained upon calculation of various rolling schedules and comparison of their total rolling times.

In this connection, it was tried to estimate the totai rolling times of various. rolling schedules by gradually reducing the rolling torque limit starting from the possible maximum value or the maximum motor torque limit which is generally 225 percent of a normal motor torque, assuming that a determined ingot is rolled to a determined slab, and as the results of above FIG. 7 was obtained.

ln H6. 7, the abscissa represents the rolling torque limit, which is to be smaller than 225 percent of a normal motor torque, and the ordinate represents the total rolling time. The numerals in the Figure show the numbers of passes.

From FIG. 7, we can understand the following facts: if the rolling torque limit is lowered, the number of passes is increased resulting in a positive increase of the total rolling time. However, as far as the number of passes is not increased, a schedule based upon a lower rolling torque limit provides a better result or a shorter total rolling time, and in fact, the schedule corresponding to point A in FIG. 7, Le, the lowest rolling torque limit which can be used for the smallest number of passes provides the shortest total rolling time. In other words, it is always said that a schedule which had been obtained just before the number of passes was increased in a process of calculating a series of schedules by gradually lowering the rolling torque limit starting from the maximum value thereof or 225 percent of a normal motor torque is the one which provides a shortest rolling time.

Furthermore, we found that the value of the rolling torque limit which provides the shortest rolling time is transferred as A, B, C in FIG. 8 according to changes of the resistance to deformation of steel materials. In FIG. 8, curve a shows a change of the total rolling time of a material of a standard resistance to deformation and provides the optimum point A. However, if the resistance to deformation is larger, curve b comes under the case, wherein point B is the optimum point. lf the resistance to deformation is smaller, point C of curve c becomes the optimum point.

Furthermore, if the limit of reduction rate is changed in a same rolling condition, the point which provides the optimum rolling schedule shifts as point A, B or C, as shown in FlG. 9, wherein curve a shows a case of a higher limit of reduction rate and provides a shortest time A, while if the limit of reduction rate is somewhat lowered, it shifts to curve b showing a longer shortest time B. If the limit of reduction is further lowered, curve 0 comes under the case with a much increased shortest-time C.

Thus, it is understood that an optimum rolling schedule which accomplishes a shortest rolling time differs as the resistance to deformation and/or the limit of reduction ratechanges.

As described in the above, an optimum schedule which accomplishes a shortest rolling time can be obtained by calculating a series of rolling schedules with gradually lowered rolling torque limits starting from the maximum torque allowable for a driving motor and selecting a schedule which had been calculated just before the number of passes was increased in the calculating process. In this calculating process, if each amount of reduction of the rolling torque limit-is selected to be very small, the strict optimum points such as shown in F IGS. 7 to 9 can be obtained. However, in that case the number of times of calculation increases and it requires a long time for the calculation.

The determination of a schedule for the subsequent passes based upon the actual resistance to deformation of an ingot detected during the initial passes must be finished by the end of the initial passes and therefore, the number of times of calculation which is allowable during the initial passes or the amount of successive diminution of the rolling torque limit is determined from the above-mentioned requirement. According to our experiences, it is found to be preferable to select the amount of reduction of the rolling torque limit at the horizontal roll stand to be 15 to 20 percent of the maximum motor torque, which generally results in the increase of the number of passes within three or four times of calculation. These calculations can generally be finished within about 2 seconds, though it largely depends upon the processing machines.

ln an example experienced by us, the first and second passes were taken as the initial passes, and in the beginning an initial rolling schedule for these two passes was determined based upon a standard value of the resistance to deformation. Then, actual rolling operation of an ingot was performed according to the initial schedule, and upon detecting the actual resistance to deformation of the ingot from the actual rolling load at the horizontal roll stand and other data obtained during the second pass, a schedule for the third and subsequent passes was determined according to the above-mentioned method. As the results of this method, two passes were reduced as compared to a conventional schedule for manual operation, and this corresponds to a saving of about 10 seconds in the total roiling time.

in the above-mentioned example, the rolling operation of the third pass was started after the optimum schedule for the third and subsequent passes had been determined, and to wait the determination of the schedule, there occurred an idle time of l to 2 seconds. This idle time of course abates the effect of this method of reducing the total rolling time.

Therefore, in a second example the first three passes were taken as the initial passes, and the initial schedule therefor was determined prior to the starting of rolling operation. The actual resistance to deformation of an ingot was detected from the data obtained during the second pass as before, and based upon the actual resistance to deformationed thus obtained an optimum schedule for the fourth and subsequent passes was determined in the same manner as before. In this case, the schedule for the fourth and subsequent passes is only to be determined by the end of the third pass, and therefore, there are about six seconds available for the calculation, in which the determination of schedule can be sufficiently completed. By this method, the abovementioned idle time was avoided.

In the following, the constitution of the subsequent schedule determining means 200 is described in detail with reference to FIG. 10.

Here it is confirmed that the first to j-th passes are taken as the initial passes and the means 200 is adapted to determine the schedule for the (j+l)-th and subsequent passes.

At the instant when the actual data collecting means 150 shown in FIG. 1 has obtained the rolling load P or P at the horizontal or vertical roll stand to which a material is first introduced in the k-th pass I k j), the means 150 dispatches the signal SR for demanding the calculation of the subsequent schedule to the means 200, or in more detail, actual material section watching means 202. The means 202 receives actual data F of roll openings of the first to k-th passes or S S (1' 1 z k) from the data storing means 160 and calculates sectional dimensions thickness and width) 81-1,, of the material at the entrance of the (k+l)-th pass. Furthermore, if it is k j, since there are no actual data of roll openings in the lc+l-th to j-th pass or passes, the means 200 receives the predetermined data F of roll opening or S S m (i 1 z j) from the initial schedule storing means 110 and calculates sectional dimensions BI-I of the material at the entrance of the (j 1)-th pass, the calculated sectional dimensions being supplied to a schedule calculating means 218.

The rate of elongation E of the material at the entrance of the k-th pass is calculated from a formula E A IA where A, is sectional area of the ingot and A is sectional area of the material at the outlet of the (k1)-th pass. This E and the draft Ah at the horizontal or vertical roll stand to which the material is first introduced in the k-th pass are supplied as a signal 203 to a deformation resistance determining means 204. The means 204 is further suppled with the rolling load PK (means P or Pl/k) at the horizontal or vertical roll stand to which the material is first introduced in the k-th pass and the data A regarding the properties of the ingot, whereby the means 204 determines Formula (3) for estimating the subsequent resistance to deformation Sm of the material. The obtained Sm is supplied to the schedule calculating means 218. The means 204 also dispatches an operation starting signal 205 to a rolling torque limit setting means 206.

The means 206 is supplied with the data A regarding the properties of the ingot and the data C comprising limits of motor maximum torque r r and first sets a trial frequency counter 208 at 1 via a signal 207 and at the same time supplies maximum trial frequency L to a judging means 226. Furthermore, the means 206 supplies amounts of successive diminution of rolling torque limit ATV, A7,, to a successive diminution amount storing means 210 as a signal 209. ATV and AT are selected to be one per a few of the maximum accelerating torque of the vertical and horizontal roll stands, respectively. The means 206 also supplies nominal values of the motor torque limits r' T (These values do not necessarily coincide with 1 r to a motor torque limit storing means 212 as a signal 21 1.

Means collectively shown by numeral 220 functions as a rolling torque limit determining means, wherein a means 214 is a multiplier and means 216 is an adder. The output 217 of the means 220 or the rolling torque limits *r 7 are expressed by using the content L of the trial frequency counter 208 as follows:

mar max L'ATH where DC (i= j +1 '-M) is the draft compensating rate which is defined as the ratio of elongations at the vertical and horizontal roll stands. The draft compensating rates are really determined by the schedule calculating means 218, but since the values are not yet determined at this stage, they are assumed, and if the actual values of DC, are determined by the means 218 are not much different from the assumed values, corrections by the actual values are omitted. In FIG. 7, formula (5) means the decreasing of rolling torque by every step Ar A rH if it is a horizontal roll and ATV if it is a vertical roll) in order to obtain the value L. L'DCATV or L- A'TH orders an accelerating torque. Usually the accelerating torque should be determined within an optimum amount and so, L max is determined by following formula:

Lmax =[1-A max/Ar] where 'rA max is an accelerating torque to give the maximum acceleration.

The schedule calculating means 218 is supplied with the above-mentioned signal 217 and other data such as 3H,, S A, B and C by some conventional method, and calculates the rolling schedules for the (j-l-l )-th to last (or M-th) passes, or the roll openings S S velocities N N N draft compensating rate DC, and other data which are required for the automatic operation of the mill, the calculated data being stored in a first schedule storing means 222. In other words, in FIG. 5 as a rolling torque limit which is the only selected value shown by FIG. 5, the drafts of each passes are determined so as to satisfy the various limits and the roll outlet dimensions are checked if they are equal to the target dimensions and then the last pass number M is determined.

The means 218 dispatches the last pass number M to an optimum schedule judging means 226, whereby the means 226 is started. The means 226 is supplied with the trial frequency L from the counter 208, and if it is 1 2L L compares the last pass number M at the frequency L with the last pass number M at the frequency L-l, or M=M(L) with M'=M(Ll If M(L)=M(Ll which corresponds to the comparison of a with b in FIG. 7, the means 226 supplies M=M(L) to a passage number storing means 228 to be stored therein, and makes the content in the first schedule storing means 222 transferred via a transfer gate 223 to a second schedule storing means 224 by a signal 230 which at the same time advances the frequency number in the trial frequency counter by one. Then, the output 217 of the rolling torque limit determining means is lOlOSZ Ol93 reduced according to Formula and based upon the new reduced rolling torque limits, a new schedule is calculated by the means 218. The new calculated schedule is stored in the first schedule storing means 222, and a new pass number M is supplied to the optimum schedule judging means 226.

Here, if it is l L L and M=M(L) M'( L-l which corresponds to the comparison of b with c in FIG. 7, the schedule which had been calculated in the just preceding time and is now stored in the second schedule storing means 224 is the optimum schedule, as it has been already explained. In this case, therefore, a signal 231 is dispatched from the means 226 to a transfer gate 234 to transfer the schedule stored in the means 224 to the automatic operation control means 400.

if, however, it is still M=M(L)=M=M( L-l) even at IFL the trial of calculation is stopped, and the schedule which was calculated lastly and is stored in the first schedule storing means 222 is taken as the optimum schedule. Therefore, the means 226 dispatches a signal 232 to a transfer gate 236 to transfer the schedule stored in the means 222 to the automatic operation control means 400.

Since the amounts of successive diminution of the rolling torque limit are selected to be one per a few (:1) of the maximum accelerating torque ('r Ace r of the vertical and horizontal roll stands, accelerating torques (r 7m available at the vertical and horizontal roll stands in the operation due to the optimum schedule of L=Lop are expressed by vAcc P/" ruce mm ruce P/ HACC mm respectively.

In the above-mentioned example of a universal blooming mill as shown in FIG. 1, wherein all rolling passages are performed without 90 rotation of a material, it was found to be advantageous to select the first to second or third passes as the initial passes and to determine a schedule for the third or fourth to last passages based upon the actual resistance to deformation of the material obtained in the second pass so that the rolling time of the subsequent passes becomes shortest. However, in case of blooming mills wherein a material to be rolled is rotated 90 in the initial passes, there will be other methods of selecting the initial passes and the pass during which the resistance to deformation is measured.

It will be appreciated from the forgoing that this invention provides a method of and an apparatus for determining an optimum rolling schedule, which is generally applicable to reversible hot rolling mills and improves the rolling efficiencies thereof.

In the term of rolling schedule used in the above are not only included the roll opening but also the entry speed, maximum rolling speed, delivery speed, acceleration and draft compensating rate of a material and all other data required for the control of rolling mills, and therefore, it may be called the schedule of operation. If such a schedule of operation is given to an automatic operation control means of a rolling mill, a fully automated operation of the rolling mill is performed with the highest efficiency thereof.

We claim:

1. A method of determining an optimum schedule of operation for reversible hot rolling mills comprising the steps of determining an initial schedule of operation for initial passes based upon the properties of a material to he rolled, rolling conditions and standard resistance to deformation of material; performing the rolling operation of the initial passes; obtaining the actual resistance to deformation from the actual rolling load or torque and roll opening in the initial passes; and determining such an optimum schedule of operation for subsequent passes that the optimum schedule provides a shortest total rolling time said optimum schedule being determined in a manner that a series of schedules are calculated by successively reducing rolling torque limit by a predetermined amount starting from a maximum motor torque of the roll and a schedule which was calculated just before a number of passes is increased is determined to be the optimum schedule.

2,. A method according to claim 1, wherein the resistance to deformation is assumed to be a known function of the rate of elongation of the material except a constant which depends upon the kind and soaking temperature of the material.

3. A method according to claim 2, wherein the constant is determined from the actual resistance to deformation and the rate of elongation obtained in the initial passes.

4. An apparatus for determining an optimum schedule of operation for reversible hot rolling mills comprising means for determining an initial schedule of operation for initial passes based upon the properties of a material to be rolled, rolling conditions and standard resistance to deformation of the material; means for measuring the actual rolling load or torque and roll opening in the initial passes; means for calculating the actual resistance to deformation of the material from the actual rolling load or torque and roll opening; and means for determining such an optimum schedule of operation for subsequent passes that the optimum schedule provides a shortest total rolling time said means for determining the optimum schedule of operation for the subsequent passes including means for calculating a series of schedules by successively reducing rolling torque limit by a predetermined amount starting from a maximum motor torque of the roll and means for checking the number of passes in each one of the series of schedules to select the optimum schedule which was calculated just before the number of passes is increased.

5. The method of claim it, wherein the calculation required to determine the optimum schedule of rolling operation is made during the initial passes, thereby shortening the rolling time.

6. The method of claim 5, wherein the initial passes include three passes and the actual resistance to deformation of the material to be rolled is determined during the second pass.

7. The method of claim 6, wherein the elongation of the material to be rolled is determined during the second pass and the resistance to deformation occur- 0 ring during the subsequent passes is predicted based on UNETED STATES PATENT aormtt (JERTEFEQATE GE QQRREQTWN Patent N Dated 5 Invent r( MINAMI, TOHRU, ET, AL.

It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

On the cover sheet {73] "Hitachi, Ltd and Yowata Iron & Steel Co Ltd. Tokyo, Japan" should read Hitachi, Ltd., and Nippon Steel Corporation, Tokyo, Japan Signed and sealed this 25th day of December" 1973 (SEAL) Attest:

EDWARD Ma FLETCHER,JR. RENE D. TEGTMEYER Attesting Officer Acting Commissioner of Patents "ORM PO-IOSO (10-69) USCOMM-DC 60376-P69 a us. GOVERNMENT PRINTING OFFICE: I959 muse-3:4,] I 

1. A method of determining an optimum schedule of operation for reversible hot rolling mills comprising the steps of determining an initial schedule of operation for initial passes based upon the properties of a material to be rolled, rolling conditions and standard resistance to deformation of material; performing the rolling operation of the initial passes; obtaining the actual resistance to deformation from the actual rolling load or torque and roll opening in the initial passes; and determining such an optimum schedule of operation for subsequent passes that the optimum schedule provides a shortest total rolling time , said optimum schedule being determined in a manner that a series of schedules are calculated by successively reducing rolling torque limit by a predetermined amount starting from a maximum motor torque of the roll and a schedule which was calculated just before a number of passes is increased is determined to be the optimum schedule.
 2. A method according to claim 1, wherein the resistance to deformation is assumed to be a known function of the rate of elongation of the material except a constant which depends upon the kind and soaking temperature of the material.
 3. A method according to claim 2, wherein the constant is determined from the actual resistance to deformation and the rate of elongation obtained in the initial passes.
 4. An apparatus for determining an optimum schedule of operation for reversible hot rolling mills comprising means for determining an initial schedule of operation for initial passes based upon the properties of a material to be rolled, rolling conditions and standard resistance to deformation of the material; means for measuring the actual rolling load or torque and roll opening in the initial passes; means for calculating the actual resistance to deformation of the material from the actual rolling load or torque and roll opening; and means for determining such an optimum schedule of operation for subsequent passes that the optimum schedule provides a shortest total rolling time , said means for determining the optimum schedule of operation for the subsequent passes including means for calculating a series of schedules by successively reducing rolling torque limit by a predetermined amount starting from a maximum motor torque of the roll and means for checking the number of passes in each one of the series of schedules to select the optimum schedule which was calculated just before the number of passes is increased.
 5. The method of claim 1, wherein the calculation required to determine the optimum schedule of rolling operation is made during the initial passes, thereby shortening the rolling time.
 6. The method of claim 5, wherein the initial passes include three passes and the actual resistance to deformation of the material to be rolled is determined during the second pass.
 7. The method of claim 6, wherein the elongation of the material to be rolled is determined during the second pass and the resistance to deformation occurring during the subsequent passes is predicted based on the assumption that the resistance to deformation is a function of the rate of elongation with the exception of a constant dependent on the kind of material being rolled and the soaking temperature of the material, said constant being determined from the actual resistance to deformation and the elongation of the material during the second pass. 